The version installed is conflicting with the version required in
testtools-1.7

ceilometer installs tooz which installs zake which has a run time
dependency on uncapped testtools. Which in turn requires a version of
unittest2 that conflicts with the version provided via packages

We need the fix to stable/juno to unbreak master because grenade.

Change-Id: Ia585d076982e1a0fbb286b7bd1845e4f9821ed76
Depends-On: Ib193e18afbb60c43d8dd66444bbf367689837182
Partial-Bug: #1430592